Flame retardant composites

ABSTRACT

A flame retardant polymer composite is disclosed. The composite includes a polymer base material and a flame retardant filler provided in the polymer base material, the flame retardant filler containing seeded boehmite particulate material having an aspect ratio of not less than 3:1

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is (i) a continuation-in-part application of U.S.patent application Ser. No. 10/414,590, filed Apr. 16, 2003, which inturn is a non-provisional application of U.S. Provisional Application60/374,014 filed Apr. 19, 2002, and (ii) a continuation-in-partapplication of U.S. patent application Ser. No. 10/823,400, filed Apr.13, 2004, and (iii) a continuation-in-part of U.S. patent applicationSer. No. 10/845,764, filed May 14, 2004. Priority to the foregoingapplications is hereby claimed, and the subject matter thereof herebyincorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention is generally directed to flame retardantcomposites, and more particularly to flame retardant composites thatinclude a polymer base material and a flame retardant filler to improveflame retardancy.

2. Description of the Related Art

With rapid improvement in technology over the past decades, increasingdemand has been created for high performance materials, includingceramics, metals and polymers for a myriad of applications. For example,in the context of microelectronic devices, market pressures dictatesmaller, faster and more sophisticated end products, which occupy lessvolume and operate at higher current densities. These higher currentdensities further increase heat generation and, often, operatingtemperatures. In this context, it has become increasingly important forsafety concerns to implement microelectronic packaging materials thatprovide exemplary flame resistance. Use of flame resistant packagingmaterials is but one example among many in which product designers havespecified use of flame resistant materials. For example, flame resistantthermoplastic polymers are in demand as construction materials.

In addition, governmental regulatory bodies have also sought flameresistant materials in certain applications to meet ever-increasingsafety concerns. Accordingly, the industry has continued to demandimproved composite materials, for example, improved polymer-basedmaterials that have desirable flame retardant characteristics.

SUMMARY

According to an aspect of the present invention, a flame retardantpolymer composite is provided. The composite includes a polymer basematerial and a flame retardant filler provided in the polymer basematerial, the flame retardant filler containing seeded boehmiteparticulate material having an aspect ratio of not less than 2:1,typically not less than 3:1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 illustrates a process flow for forming a polymer compositeaccording to an embodiment of the present invention.

FIG. 2 illustrates a thermogravimetric analysis (TGA) of seeded boehmitevs. conventional ATH.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

According to one aspect of the present invention, a flame retardantpolymer composite is provided, which includes a polymer base materialand a flame retardant filler. Notably the flame retardant fillerincludes a seeded boehmite particulate material having an aspect ratioof not less than about 3:1. Typically, the polymer based material is amaterial that has commercial significance and demand in industry, butoftentimes does not exhibit native flame retardant properties.Quantitatively, flame retardancy may be measured according tounderwriter laboratories test UL 94, the so called vertical burn test.The UL 94 test is carried out by ASTM D635 standards, and materials aregiven a V rating based upon several observed characteristics includingflame time, glow time, extent of burning, as well as the ability of thesample to ignite cotton. Typically, the polymer based materials ofinterest and in need of flame retardant characteristics have a UL 94rating of V-2 or above, indicating volatility under certain conditions.Additional features of the polymer base material according toembodiments of the present invention are discussed below. First, we turnto the flame retardant filler, particularly, the seeded boehmiteparticulate material according to embodiments of the present inventionthat contributes to significant improvement in flame retardancy.

According to a particular feature, the seeded boehmite particulatematerial is utilized rather than boehmite derived from non-seededprocessing pathways, including non-seeded hydrothermal treatment andprecipitation pathways. As discussed in more detail below, embodimentsof the present invention have demonstrated exemplary flame retardancy,even without relying on additional flame retardant components to improveperformance.

Seeded boehmite particulate material is generally formed by a processthat includes providing a boehmite precursor and boehmite seeds in asuspension, and heat treating (such as by hydrothermal treatment) thesuspension (alternatively sol or slurry) to convert the boehmiteprecursor into boehmite particulate material formed of particles orcrystallites. According to a particular aspect, the boehmite particulatematerial has a relatively elongated morphology, described generallyherein in terms of aspect ratio, described below.

The term “boehmite” is generally used herein to denote alumina hydratesincluding mineral boehmite, typically being Al₂O₃.H₂O and having a watercontent on the order of 15%, as well as psuedoboehmite, having a watercontent higher than 15%, such as 20-38% by weight. It is noted thatboehmite (including psuedoboehmite) has a particular and identifiablecrystal structure, and accordingly unique X-ray diffraction pattern, andas such, is distinguished from other aluminous materials including otherhydrated aluminas such as ATH (aluminum trihydroxide) a common precursormaterial used herein for the fabrication of boehmite particulatematerials.

The aspect ratio, defined as the ratio of the longest dimension to thenext longest dimension perpendicular to the longest dimension, isgenerally not less than 2:1, and preferably not less than 3:1, 4:1, or6:1. Indeed, certain embodiments have relatively elongated particles,such as not less than 9:1, 10:1, and in some cases, not less than 14:1.With particular reference to needle-shaped particles, the particles maybe further characterized with reference to a secondary aspect ratiodefined as the ratio of the second longest dimension to the thirdlongest dimension. The secondary aspect ratio is generally not greaterthan 3:1, typically not greater than 2:1, or even 1.5:1, and oftentimesabout 1:1. The secondary aspect ratio generally describes thecross-sectional geometry of the particles in a plane perpendicular tothe longest dimension.

Platey or platelet-shaped particles generally have an elongatedstructure having the aspect ratios described above in connection withthe needle-shaped particles. However, platelet-shaped particlesgenerally have opposite major surfaces, the opposite major surfacesbeing generally planar and generally parallel to each other. Inaddition, the platelet-shaped particles may be characterized as having asecondary aspect ratio greater than that of needle-shaped particles,generally not less than about 3:1, such as not less than about 6:1, oreven not less than 10:1. Typically, the shortest dimension or edgedimension, perpendicular to the opposite major surfaces or faces, isgenerally less than 50 nanometers.

Morphology of the seeded boehmite particulate material may be furtherdefined in terms of particle size, more particularly, average particlesize. Here, the seeded boehmite particulate material, that is, boehmiteformed through a seeding process (described in more detail below) has arelatively fine particle or crystallite size. Generally, the averageparticle size is not greater than about 1000 nanometers, and fall withina range of about 100 to 1000 nanometers. Other embodiments have evenfiner average particle sizes, such as not greater than about 800nanometers, 600 nanometers, 500 nanometers, 400 nanometers, and evenparticles having an average particle size smaller than 300 nanometers,representing a fine particulate material. In certain embodiments, theaverage particle size was less than 200 nanometers, such as within arange of about 100 nanometers to about 150 nanometers.

As used herein, the “average particle size” is used to denote theaverage longest or length dimension of the particles. Due to theelongated morphology of the particles, conventional characterizationtechnology is generally inadequate to measure average particle size,since characterization technology is generally based upon an assumptionthat the particles are spherical or near-spherical. Accordingly, averageparticle size was determined by taking multiple representative samplesand physically measuring the particle sizes found in representativesamples. Such samples may be taken by various characterizationtechniques, such as by scanning electron microscopy (SEM).

The present seeded boehmite particulate material has been found to havea fine average particle size, while oftentimes competing non-seededbased technologies are generally incapable of providing such fineaverage particle sizes in the context of anisotropic particles. In thisregard, it is noted that oftentimes in the literature, reported particlesizes are not set forth in the context of averages as in the presentspecification, but rather, in the context of nominal range of particlesizes derived from physical inspection of samples of the particulatematerial. Accordingly, the average particle size will lie within thereported range in the prior art, generally at about the arithmeticmidpoint of the reported range, for the expected Gaussian particle sizedistribution. Stated alternatively, while non-seeded based technologiesmay report fine particle size, such fine sizing generally denotes thelower limit of an observed particle size distribution and not averageparticle size.

Likewise, in a similar manner, the above-reported aspect ratiosgenerally correspond to the average aspect ratio taken fromrepresentative sampling, rather than upper or lower limits associatedwith the aspect ratios of the particulate material. Oftentimes in theliterature, reported particle aspect ratios are not set forth in thecontext of averages as in the present specification, but rather, in thecontext of nominal range of aspect ratios derived from physicalinspection of samples of the particulate material. Accordingly, theaverage aspect ratio will lie within the reported range in the priorart, generally at about the arithmetic midpoint of the reported range,for the expected Gaussian particle morphology distribution. Statedalternatively, while non-seeded based technologies may report aspectratio, such data generally denotes the lower limit of an observed aspectratio distribution and not average aspect ratio.

In addition to aspect ratio and average particle size of the particulatematerial, morphology of the particulate material may be furthercharacterized in terms of specific surface area. Here, the commonlyavailable BET technique was utilized to measure specific surface area ofthe particulate material. According to embodiments herein, the boehmiteparticulate material has a relatively high specific surface area,generally not less than about 10 m²/g, such as not less than about 50m²/g, 70 m²/g, or not less than about 90 m²/g. Since specific surfacearea is a function of particle morphology as well as particle size,generally the specific surface area of embodiments was less than about400 m²/g, such as less than about 350 or 300 m²/g.

Turning to the details of the processes by which the boehmiteparticulate material may be manufactured, generally ellipsoid, needle,or platelet-shaped boehmite particles are formed from a boehmiteprecursor, typically an aluminous material including bauxitic minerals,by hydrothermal treatment as generally described in the commonly ownedpatent described above, U.S. Pat. No. 4,797,139. More specifically, theboehmite particulate material may be formed by combining the boehmiteprecursor and boehmite seeds in suspension, exposing the suspension(alternatively sol or slurry) to heat treatment to cause conversion ofthe raw material into boehmite particulate material, further influencedby the boehmite seeds provided in suspension. Heating is generallycarried out in an autogenous environment, that is, in an autoclave, suchthat an elevated pressure is generated during processing. The pH of thesuspension is generally selected from a value of less than 7 or greaterthan 8, and the boehmite seed material has a particle size finer thanabout 0.5 microns. Generally, the seed particles are present in anamount greater than about 1% by weight of the boehmite precursor(calculated as Al₂O₃), and heating is carried out at a temperaturegreater than about 120° C., such as greater than about 125° C., or evengreater than about 130° C., and at a pressure greater than about 85 psi,such as greater than about 90 psi, 100 psi, or even greater than about110 psi.

The particulate material may be fabricated with extended hydrothermalconditions combined with relatively low seeding levels and acidic pH,resulting in preferential growth of boehmite along one axis or two axes.Longer hydrothermal treatment may be used to produce even longer andhigher aspect ratio of the boehmite particles and/or larger particles ingeneral.

Following heat treatment, such as by hydrothermal treatment, andboehmite conversion, the liquid content is generally removed, such asthrough an ultrafiltration process or by heat treatment to evaporate theremaining liquid. Thereafter, the resulting mass is generally crushed,such to 100 mesh. It is noted that the particulate size described hereingenerally describes the single crystallites formed through processing,rather than the aggregates which may remain in certain embodiments(e.g., for those products that call for and aggregated material).

According to data gathered by the present inventors, several variablesmay be modified during the processing of the boehmite raw material, toeffect the desired morphology. These variables notably include theweight ratio, that is, the ratio of boehmite precursor to boehmite seed,the particular type or species of acid or base used during processing(as well as the relative pH level), and the temperature (which isdirectly proportional to pressure in an autogenous hydrothermalenvironment) of the system.

In particular, when the weight ratio is modified while holding the othervariables constant, the shape and size of the particles forming theboehmite particulate material are modified. For example, when processingis carried at 180° C. for two hours in a 2 weight % nitric acidsolution, a 90:10 ATH:boehmite seed ratio forms needle-shaped particles(ATH being a species of boehmite precursor). In contrast, when theATH:boehmite seed ratio is reduced to a value of 80:20, the particlesbecome more elliptically shaped. Still further, when the ratio isfurther reduced to 60:40, the particles become near-spherical.Accordingly, most typically the ratio of boehmite precursor to boehmiteseeds is not less than about 60:40, such as not less than about 70:30 or80:20. However, to ensure adequate seeding levels to promote the fineparticulate morphology that is desired, the weight ratio of boehmiteprecursor to boehmite seeds is generally not greater than about 99:1, or98:2. Based on the foregoing, an increase in weight ratio generallyincreases aspect ratio, while a decrease in weight ratio generallydecreased aspect ratio.

Further, when the type of acid or base is modified, holding the othervariables constant, the shape (e.g., aspect ratio) and size of theparticles are affected. For example, when processing is carried out at100° C. for two hours with an ATH:boehmite seed ratio of 90:10 in a 2weight % nitric acid solution, the synthesized particles are generallyneedle-shaped, in contrast, when the acid is substituted with HCl at acontent of 1 weight % or less, the synthesized particles are generallynear spherical. When 2 weight % or higher of HCl is utilized, thesynthesized particles become generally needle-shaped. At 1 weight %formic acid, the synthesized particles are platelet-shaped. Further,with use of a basic solution, such as 1 weight % KOH, the synthesizedparticles are platelet-shaped. If a mixture of acids and bases isutilized, such as 1 weight % KOH and 0.7 weight % nitric acid, themorphology of the synthesized particles is platelet-shaped.

Suitable acids and bases include mineral acids such as nitric acid,organic acids such as formic acid, halogen acids such as hydrochloricacid, and acidic salts such as aluminum nitrate and magnesium sulfate.Effective bases include, for example, amines including ammonia, alkalihydroxides such as potassium hydroxide, alkaline hydroxides such ascalcium hydroxide, and basic salts.

Still further, when temperature is modified while holding othervariables constant, typically changes are manifested in particle size.For example, when processing is carried out at an ATH:boehmite seedratio of 90:10 in a 2 weight % nitric acid solution at 150° C. for twohours, the crystalline size from XRD (x-ray diffractioncharacterization) was found to be 115 Angstroms. However, at 160° C. theaverage particle size was found to be 143 Angstroms. Accordingly, astemperature is increased, particle size is also increased, representinga directly proportional relationship between particle size andtemperature.

The following examples focus on seeded boehmite synthesis.

Example 1 Plate-Shaped Particle Synthesis

An autoclave was charged with 7.42 lb. of Hydral 710 aluminumtrihydroxide purchased from Alcoa; 0.82 lb of boehmite obtained fromSASOL under the name—Catapal B pseudoboehmite; 66.5 lb of deionizedwater; 0.037 lb potassium hydroxide; and 0.18 lb of 22 wt % nitric acid.The boehmite was pre-dispersed in 5 lb of the water and 0.18 lb of theacid before adding to the aluminum trihydroxide and the remaining waterand potassium hydroxide.

The autoclave was heated to 185° C. over a 45 minute period andmaintained at that temperature for 2 hours with stirring at 530 rpm. Anautogenously generated pressure of about 163 psi was reached andmaintained. Thereafter the boehmite dispersion was removed from theautoclave. After autoclave the pH of the sol was about 10. The liquidcontent was removed at a temperature of 65° C. The resultant mass wascrushed to less than 100 mesh. The SSA of the resultant powder was about62 m²/g. Average particle size (length) was within a range of about 150to 200 nm according to SEM image analysis.

Example 2 Needle-Shaped Particle Synthesis

An autoclave was charged with 250 g of Hydral 710 aluminum trihydroxidepurchased from Alcoa; 25 g of boehmite obtained from SASOL under thename—Catapal B pseudoboehmite; 1000 g of deionized water; and 34.7 g of18% nitric acid. The boehmite was pre-dispersed in 100 g of the waterand 6.9 g of the acid before adding to the aluminum trihydroxide and theremaining water and acid.

The autoclave was heated to 180° C. over a 45 minute period andmaintained at that temperature for 2 hours with stirring at 530 rpm. Anautogenously generated pressure of about 150 psi was reached andmaintained. Thereafter the boehmite dispersion was removed from theautoclave. After autoclave the pH of the sol was about 3. The liquidcontent was removed at a temperature of 95° C. The resultant mass wascrushed to less than 100 mesh. The SSA of the resultant powder was about120 m²/g. Average particle size (length) was within a range of about 150to 200 nm according to SEM image analysis.

Example 3 Ellipsoid Shaped Particle Synthesis

An autoclave was charged with 220 g of Hydral 710 aluminum trihydroxidepurchased from Alcoa; 55 g of boehmite obtained from SASOL under thename—Catapal B pseudoboehmite; 1000 g of deionized water; and 21.4 g of18% nitric acid. The boehmite was pre-dispersed in 100 g of the waterand 15.3 g of the acid before adding to the aluminum trihydroxide andthe remaining water and acid.

The autoclave was heated to 172° C. over a 45 minute period andmaintained at that temperature for 3 hours with stirring at 530 rpm. Anautogenously generated pressure of about 120 psi was reached andmaintained. Thereafter the boehmite dispersion was removed from theautoclave. After autoclave the pH of the sol was about 4. The liquidcontent was removed at a temperature of 95° C. The resultant mass wascrushed to less than 100 mesh. The SSA of the resultant powder was about135 m²/g. Average particle size (length) was within a range of about 150to 200 nm according to SEM image analysis.

Example 4 Near Spherical Particle Synthesis

An autoclave was charged with 165 g of Hydral 710 aluminum trihydroxidepurchased from Alcoa; 110 g of boehmite obtained from SASOL under thename—Catapal B pseudoboehmite; 1000 g of deionized water; and 35.2 g of18% nitric acid. The boehmite was pre-dispersed in 100 g of the waterand 30.6 g of the acid before adding to the aluminum trihydroxide andthe remaining water and acid.

The autoclave was heated to 160° C. over a 45 minute period andmaintained at that temperature for 2.5 hours with stirring at 530 rpm.An autogenously generated pressure of about 100 psi was reached andmaintained. Thereafter the boehmite dispersion was removed from theautoclave. After autoclave the pH of the sol was about 3.5. The liquidcontent was removed at a temperature of 95° C. The resultant mass wascrushed to less than 100 mesh. The SSA of the resultant powder was about196 m²/g.

Turning to the polymer base material of the composite, the material maybe formed of polymers including elastomeric materials, such aspolyolefins, polyesters, fluoropolymers, polyamides, polyimides,polycarbonates, polymers containing styrene, epoxy resins, polyurethane,polyphenyl, silicone, or combinations thereof. In one exemplaryembodiment, the polymer composite is formed of silicone, siliconeelastomer, and silicone gels. Silicone, silicone elastomer, and siliconegels may be formed using various organosiloxane monomers havingfunctional groups such as alkyl groups, phenyl groups, vinyl groups,glycidoxy groups, and methacryloxy groups and catalyzed usingplatinum-based or peroxide catalyst. Exemplary silicones may includevinylpolydimethylsiloxane, polyethyltriepoxysilane, dimethyl hydrogensiloxane, or combinations thereof. Further examples include aliphatic,aromatic, ester, ether, and epoxy substituted siloxanes. In oneparticular embodiment, the polymer composite comprisesvinylpolydimethylsiloxane. In another particular embodiment, the polymercomposite comprises dimethyl hydrogen siloxane. Silicone gels are ofparticular interest for tackiness and may be formed with addition of adiluent.

Aspects of the present invention are particularly useful for polymerbase materials that do not have a native, robust flame retardancy, suchas those polymers that have a flame retardancy of V-2 or greater. Forexample, Nylon 6, noted below, has been characterized as having a nativeflame retardancy of V-2. Accordingly, as a subset of polymers thatbenefit from flame retardancy additives according to aspects of thepresent invention include: non-chlorinated polymers, non-fluorinatedpolymers, and may be selected from the group consisting of polyolefins,polyesters, polyamides, polyimides, polycarbonates, polymers containingstyrene, epoxy resins, polyurethane, polyphenyl, and combinationsthereof.

The polymer composite may comprise at least about 0.5 to about 50 wt %boehmite particulate material, such as about 2 to about 30 wt %.According to one feature, exemplary flame retardancy may be achievedeven a low loadings, such as within a range of about 2 to 15 wt % of thetotal composite.

Oftentimes the composite material is in the form of a component (curedform), and may find practical use as a polymer structural component suchas a construction material. Typically, the polymer base material iscombined with the boehmite filler material to form the composite, suchas by mixing the components and, in the case of structural components,followed shape forming. Shape forming would not be required in the caseof coating compositions.

Turning to FIG. 1, a process for forming a polymer component in which apolymer base component is combined with boehmite. In the particularprocess flow, a molded polymer component is formed by injection molding.FIG. 1 details the process flow for nylon 6-based polymer component thatmay take on various contours and geometric configurations for theparticular end use. As described, nylon-6 raw material is first dried,followed by premixing with boehmite under various loading levels. Thepremixed nylon-boehmite is then extruded to form pelletized extrudates,which are then cooled and dried. The final article is then formed byinjection molding, the pelletized extrudates providing the feedstockmaterial for the molding process. The particular geometric configurationmay vary widely depending upon the end use, but here, flat bars wereextruded that were then used as test samples for flame retardancy.

Following the foregoing process flow, two different filler loadinglevels were selected for flame retardancy testing, 3 wt. % and 5 wt. %of needle shaped (alternatively referred to as whisker or rod-shaped)fine boehmite. The samples were tested according to UL 94V, utilizingthe classifying criteria below in Table 1. TABLE 1 Criteria Conditions94 V-0 94 V-1 94 V-2 Flame time, T1 or T2 ≦10 s ≦30 s  ≦30 s  FlameTime, T1 + T2 ≦50 s ≦250 s ≦250 s Glow Time, T3 ≦30 s ≦60 s  ≦60 s  Didsample burn to No No No holding clamp? yes/no Did sample ignite No NoYes cotton? Yes/no

As a result of testing, both the 3 wt. % and 5 wt. % loading levelsprovided the highly desirable V-0 rating. Such exemplary flameretardancy is notable, for various reasons. For example, the V-0 ratingwas achieved at very moderate loading levels, and without inclusion ofadditional flame retardant fillers. It should be noted, however, thatadditional fillers may be incorporated in certain embodiments to achieveadditional flame retardancy, although the particular seeded boehmitematerial described above provides a marked improvement in flameretardancy without relying upon additional fillers.

The above-reported flame retardancy takes on even additionalsignificance when compared to the state of the art. For example, otherreports have been provided in which fine boehmite material has only beenable to provide limited flame retardancy, and not V-0 as reportedherein. However, the boehmite additives utilized in these other reportsis generally not a seeded boehmite, and is formed through a non-seededprocess, including non-seeded hydrothermal processing pathways, or byprecipitation. While not wishing to be bound by any particular theory,it is believed that the seeded processing pathway contributes to theexemplary flame retardancy reported herein. One possible explanation forthis is that the seeded boehmite material has unique morphologicalfeatures, perhaps even beyond the morphologies described above inconnection with primary and secondary aspect ratios forming elongatedplatelet and needle-shaped particulates. However, it is additionallybelieved that the high aspect ratio morphologies enabled by seededprocessing pathway may also further contribute to the exemplary flameretardancy. The high aspect ratio particles may provide a serpentine ortortuous pathway for oxygen migration, thereby inhibiting flamepropagation due to reduced oxygen migration to the flame front or area.

Turning to FIG. 2, the results of thermogravimetric analysis (TGA) arereported for whisker (needle) shaped boehmite, as compared toconventional ATH. As shown, the needle-shaped boehmite particulatematerial loses crystalline (as opposed to adsorbed or absorbed) water atlower temperatures and continues losing water at temperatures above ATH,extending into the 500° C. range. The dynamics associated with waterloss associated with the seeded boehmite particulate material may alsopartially explain the flame retardancy characteristics reported herein.

While the foregoing has focused on polymer composite components, such asstructural components, it is also noted that the polymer composite mayalso be in the form of a surface coating solution, such as apolymer-containing paint formulation. Of course, like the polymercomponent described above, the flame retardancy characteristics aregenerally associated with the cured material. Accordingly, in the caseof surface coating solutions, flame retardancy is associated with thecured, dried coating. For additional details of surface coatingsolutions, the reader is directed to co-pending U.S. patent applicationSer. No. 10/823,400, filed Apr. 13, 2004, Attorney Docket Number1055-A4363, incorporated herein by reference.

According to a further aspect of the invention, the flame retardantfiller may also be in the form of a blend of flame retardant components,including iron oxide, and a vitrifying component, such as metal borates,preferably zinc borate, along with the seeded boehmite particulatematerial described in detail above. Conventional ATH may also beincorporated. Other filler may include materials such as glass fibers,nano-clays, alumina (e.g., submicron alpha alumina), and carbon.

The polymer composite may further include thermally conductive fillers,such as alumina and boron nitride. As a result, the composite may have athermal conductivity not less than about 0.5 W/m-K, such as not lessthan 1.0 W/m-K or not less than 2.0 W/m-K, particularly suitable forapplications requiring a thermal transfer performance, such as a thermalinterface material used in microelectronic applications.

While the invention has been illustrated and described in the context ofspecific embodiments, it is not intended to be limited to the detailsshown, since various modifications and substitutions can be made withoutdeparting in any way from the scope of the present invention. Forexample, additional or equivalent substitues can be provided andadditional or equivalent production steps can be employed. As such,further modifications and equivalents of the invention herein disclosedmay occur to persons skilled in the art using no more than routineexperimentation, and all such modifications and equivalents are believedto be within the scope of the invention as defined by the followingclaims.

1. A flame retardant polymer composite, comprising: a polymer basematerial; and a flame retardant filler provided in the polymer basematerial, the flame retardant filler comprising seeded boehmiteparticulate material having an aspect ratio of not less than 3:1.
 2. Thecomposite of claim 1, wherein the composite has a flame retardancy ofV-0 or V-1 according to UL94
 3. The composite of claim 2, wherein thecomposite has a flame retardancy of V-0.
 4. The composite of claim 2,wherein the composite has said flame retardancy in cured form.
 5. Thecomposite of claim 4, wherein the composite is a polymer component. 6.The composite of claim 4, wherein the composite is in the form of asurface coating solution, the composite having said flame retardancy incoated form.
 7. The composite of claim 1, wherein the polymer basematerial has a flame retardancy of V-2 or higher, the filler functioningto improve the flame retardancy to composite to V-1 or V-0 according toUL
 94. 8. The composite of claim 1, wherein the polymer base material isselected from the group consisting of polyolefins, polyesters,fluoropolymers, polyamides, polyimides, polycarbonates, polymerscontaining styrene, epoxy resins, polyurethane, polyphenyl, silicone,and combinations thereof.
 9. The composite of claim 8, wherein thepolymer base material is a non-chlorinated polymer and is anon-fluorinated polymer, and is selected from the group consisting ofpolyolefins, polyesters, polyamides, polyimides, polycarbonates,polymers containing styrene, epoxy resins, polyurethane, polyphenyl, andcombinations thereof.
 10. (canceled)
 11. (canceled)
 12. (canceled) 13.(canceled)
 14. (canceled)
 15. The composite of claim 1, wherein thecomposite comprises about 0.5 to 50.0 wt % flame retardant filler. 16.The composite of claim 15, wherein the composite comprises about 2.0 to30.0 wt % flame retardant filler.
 17. The composite of claim 16, whereinthe composite comprises about 2.0 to 15.0 wt % flame retardant filler.18. The composite of claim 1, wherein the seeded boehmite particulatematerial has an aspect ratio of not less than 4:1.
 19. The composite ofclaim 1, wherein the seeded boehmite particulate material has an aspectratio of not less than 6:1.
 20. (canceled)
 21. The composite of claim 1,wherein the seeded boehmite particulate material predominantly comprisesplatelet-shaped particles, having a secondary aspect ratio of not lessthan 3:1.
 22. (canceled)
 23. (canceled)
 24. The composite of claim 1,wherein the seeded boehmite particulate material predominantly comprisesneedle-shaped particles.
 25. The composite of claim 24, wherein theneedle-shaped particles have a secondary aspect ratio of not greaterthan 3:1.
 26. (canceled)
 27. The composite of claim 1, wherein theaverage particle size of the seeded boehmite particulate material is notgreater than 1000 nm.
 28. The composite of claim 27, wherein the averageparticle size is between about 100 and 1000 nm.
 29. (canceled) 30.(canceled)
 31. The composite of claim 28, wherein the average particlesize is not greater than 500 nm.
 32. The composite of claim 31, whereinthe average particle size is not greater than 400 nm.
 33. (canceled) 34.The composite of claim 1, wherein the boehmite particulate material hasa specific surface area of not less than about 10 m²/g.
 35. Thecomposite of claim 34, wherein the specific surface area is not lessthan about 50 m²/g.
 36. (canceled)
 37. (canceled)
 38. A method offorming a flame retardant polymer composite, comprising: providing apolymer base material; and combining a flame retardant filler with thepolymer base material to form the flame retardant polymer composite, theflame retardant filler comprising seeded boehmite particulate materialhaving an aspect ratio of not less than 3:1.
 39. The method of claim 38,further including shape forming following combining, the flame retardantcomposite being a polymer component.
 40. The method of claim 38, whereinthe flame retardant composite is a surface coating solution.
 41. Themethod of claim 38, wherein the composite has a flame retardancy of V-0or V-1 according to UL94.
 42. The method of claim 41, wherein thecomposite has a flame retardancy of V-0.
 43. The method of claim 38,wherein the polymer base material has a flame retardancy of V-2 orhigher, the filler functioning to improve the flame retardancy tocomposite to V-1 or V-0 according to UL 94.